JANCZEWKO, Poland -- On July 10, 1941, a 25-year-old Polish farm woman paused from her chores to survey the hills around her. The day was hot and windless, and over a field of rye she saw a column of black smoke rising above a town to the east. Standing in the barnyard amid the sounds of sheep and chickens, she wept.

The town in the distance was Jedwabne, and the smoke came from a barn where several hundred Jews were being burned alive by their Polish neighbors. A similar pogrom had occurred in another nearby town that...